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phase oil should be on the bottom hole, that is the bottom-hole
pressure should be higher than the saturation pressure (the samples
taken out in the zone of two-phase flow do not characterize
the formation oil). If it is impossible to provide this condition by

the corresponding change of the production conditions of the well
then the samples are taken out of shut-in wells or are prepared mixing
up oil and gas artificially in proper proportions.

Because of the considerable changeability of oil properties
within the limits of the formation for more exact estimation of its
average properties oil sampling should be conducted out of the wells
evenly placed on the deposit. Optimal amount of the samples is

determined by means of the methods of mathematical statistics
taking into account the changeability of parameters of oil throughout
the deposit and the accuracy of the equipment used for conducting

the researches.
Receiving the reliable and high-quality downhole oil sample
depends on the accordance of the sampling technology to the field
drive and on the structural peculiarities of the sampler and on its

quality as well.
To get the reliable and high-quality downhole oil sample the
sampling process and the structure of the downhole sampler should

correspond such requirements as:

1. Oil sampling should be conducted strictly at the necessary
depth under known formation pressure and temperature.
2. The sample of oil taken out of the well should characterize the
most general properties of formation oil in the sampling point, that is
to have the maximum reliability (the sample taken out of the well
should be representative). The representative sample is the formation
oil sample saturated with gas and which is located under formation

pressure and temperature.
3. The amount of the sample taken out of the well should be
sufficient in order to ensure the possibility of determination of its
properties in the laboratory (by means of AFM-300M (АСМ-300М)
installation).

4. The sampler should be of reliable tightness, and it also should
ensure the possibility of the qualitative displacement of the sample

into the container and into the equipment for researches.

The downhole sampler is put down into the well through the

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